The HW30 is a fantastic rifle. It was my main air rifle for over 40 years... I am into PCP now but if I were to go back I would buy another HW30.
Yeah. I think the HW50S, is like a lot of the Euro guns, really not designed around kids. The 30 is a bit more compact, though may still be a stretch for a youg fella to handle, esp., the cocking forces required. If you find one of the Old-School Cigar/Magazine Stores, or luck in to a Book Store that carries some import magazines, keep your eyes out for any of the Brit Airgun Magazines. Aside from that they are actually aimed at pretty much the main market there, which is adults, looking for decent quality, mainly, it is eye opening, to see the variety of air guns that are available
But I think the best idea is to research and to stick with a known AIRGUN Brand, that has a history of quality, and that will go MILES towards making the experience enjoyable, instead of frustrating. I would stay away from airguns that carry Firearm Brand Names, as they have bugger all to do with the firearm brand, beside licensing the name. Unless you know up front, what to expect, from a (most likely Chinese) import air arm.
Diana made a LOT of really nice, kids size, and decent quality rifles over the years. Shop used, buy a known name and model, and be happier at the end!